1. Field of the Invention
The present invention relates to a washing machine, and more particularly, to a brushless DC motor for driving a drum-type washing machine that reduces noise.
2. Discussion of the Related Art
Generally, drum-type washing machines and methods use a frictional force between the laundry and the water in the drum to clean laundry. A motor rotates the drum and when a wash cycle is in progress, the drum contains detergent, water and laundry. The aforementioned drum-type washing machine and method has the advantages of preventing the laundry from being damaged or tangled and also creates the effect of beating and rubbing the laundry. One example of such a drum-type washing machine with a DC motor is depicted in FIGS. 1 to 4.
FIG. 1 is a cross sectional view of a washing machine that illustrates the structure of a conventional drum-type washing machine, and FIG. 2 is an enlarged view of the cut-out “A” in FIG. 1. As shown in FIGS. 1 and 2, a tub 3 capable of storing water for washing is installed in the interior of an enclosure or cabinet 5, and is provided therein with a drum 9 for containing the laundry. The drum 9 is located in the rear portion of enclosure or cabinet 5 and is connected to a drum shaft 17 that transfers force from motor 20 to drive drum 9.
A slot 11 is mounted on a front and rear end of the drum shaft 17, and tub 3 is provided in the center of enclosure or cabinet 5 with a slot housing 15 for supporting the slot 11. A support bracket 16 is fixed to the rear wall of the tub 3, and a stator 30, which is a part of a DC motor, is fastened to the supporting bracket 16 by means of a plurality of bolts 19.
As shown in FIG. 3, the stator 30 includes a ring-shaped frame 31, and protrusions or slots 33, which have coils 33a wound around them. Protrusions or slots 33 extend radially from the outside of the frame 31. A coupling rib portion 32 is formed integrally with the frame 31, extends inwardly from the frame 31, and has a coupling hole 32a for fixing the stator 30 to the rear wall of the tub 3.
Besides the stator 30, the motor 20 includes a rotor 40 shown in FIG. 4. The rotor 40 is coupled to the rear end of the drum shaft 17 by means of a fixing bolt 18. The drum 9 is directly coupled to the rotor 40 and rotates with the rotor 40.
The enclosure or cabinet 5 has a door on its front side and is connected to gasket 2, which also connects to the tub 3. A hanging spring 4 for supporting the tub 3 in the proper position is provided between the inside of the upper surface of the enclosure or cabinet 5 and the upper side of the circumference of the tub 3. A damper 10 reduces friction and vibration generated from the tub 3 during the spin cycle. Damper 10 is located between the inside of the lower surface of the enclosure or cabinet 5 and the lower side of the circumference of the tub 3.
In a conventional DC drum-type washing machine constructed as described above, the rotor 40 is rotated by an electromagnetic force created by the power supplied to the stator 30 and a permanent magnet 41 attached to the inside of the rotor 40. The force transferred to the drum shaft 17 allows the drum 9 to rotate, thereby facilitating a washing motion.
However, the conventional DC drum-type washing machine produces unwanted noise due to air friction between the rotor 40 and the stator 30. Specifically, if the rotor 40 is rotated at a high speed, some air flows rapidly through clearance space 21 between the stator 30 and the rotor 40, while other air between the stator 30 and the protrusion or slot 33 remains stationary. Therefore, a pressure differential is created between the static and dynamic air, and the air between the protrusions or slots flows into the clearance space 21 and collides with the air rapidly flowing through the clearance space 21 to generate a loud, undesirable sound. If the frequency of the sound is the same as the natural frequency of the rotor 40 or the stator 30, resonance occurs and enhances the unwanted noise to an amplified level. In particular, as the laundry in drum 9 dries, the speed of the rotor 40 and attached drum 9 increases, thus increasing the speed of dynamic air flow and ultimately generating louder unwanted noise.
In addition, the polarity of each protrusions or slots 33 is changed at a very high speed when the motor is operational, thus, protrusion or slots 33 vibrate and can reach a frequency that further amplifies the noise.